President Obama authorizing air strikes to protect Americans there and humanitarian airdrop, food and water to help tens of thousands of Iraqis under siege by the brutal islamic militant group looking to take over Iraq and threaten America. Martha Raddatz broke the news and joins us from Washington. Good morning, Martha. Reporter: Good morning, George. It's been nearly three years since U.S. Forces left Iraq, three years since the president announced the war was over. But this morning, U.S. Warplanes are armed and ready to strike targets in Iraq on the president's order. It is a stunning turn of events. The U.S. Poised to enter a war that the president wanted to forget. But with Isis, the islamic militants seeking to topple the Iraqi government now poised to attack the key northern city of erbil where the U.S. Has a consulate and some 40 military advisers, the president said late last night he has authorized targeted air strikes. We intend to stay vigilant and take action if these terrorist forces threaten our personnel or facilities anywhere in Iraq. Reporter: The president has said there will be no U.S. Boots on the ground. I will not allow the united States to be dragged into fighting another war in Iraq. And so even as we support Iraqis as they take the fight to these terrorists, American combat troops will not be returning to fight in Iraq. Reporter: But before the president spoke last night, Americans conducted that difficult and dangerous humanitarian mission, three U.S. Air force cargo jets escorted by two f-18 fighter jets dropping critical supplies during a low-flying 15-minute pass in a race to stop a catastrophe. Tens of thousands of people who fled to the top of a mountain in sinjar now slowly dying from blistering heat, pleading that there is no water, no bread. Nearly 40 children already dead. They are trapped 3,000 feet up with no escape because down below Isis terrorists are warning of a slaughter if they return. The U.S. Aircraft dropped 5300 gallons of water and 8,000 meals ready to eat. Those missions will be ongoing since those supplies could go quickly, as for those air strikes, the president has now authorized a U.S. Official tells me that Isis is positioning itself for a rapid advance into erbil and U.S. Warplanes could be launched any time there is movement towards that city. George. Have to be ready for that. Martha, stand by. To ABC's Jon Karl at the white house. And, Jon, the president ran for office promising to end the war. Clearly reluctant to make this discussion. Clearly in an animated discussion with Denis Mcdonough after making the decision to authorize the air strikes. Not a decision he wanted to make. Reporter: You could sense the tension here at the white house yesterday, George. As he was making this decision, this is a president that is reluctant to use military force anywhere but especially in Iraq. He sees it as one of his top accomplishments as president ending America's involvement in an unpopular war but in the end the president felt that his hand was forced. It was forced because you had a humanitarian catastrophe where the U.S. Military could come in and make a difference and it was forced because that terrorist group is advancing on a city that has a large U.S. Consulate and there is a threat to Americans serving there. So in the end, the president's hand forced to make a decision that he has long resisted making. Jon, the president still going on vacation tomorrow heading up to Martha's vineyard but scheduled to return to the white house next week. Reporter: That's right. It's a two-week have a karngs at least that's what it's scheduled. Scheduled to come back for two days. White house officials won't say what the meeting is for. It's not necessarily about this but you can imagine this will be high on his agenda and as the president goes to Martha's vineyard he is taking several of his top advisers including his national security adviser Susan rice and has all the communications equipment to handle this. No president as you know, George, truly goes on vacation. That's for sure. Okay, Jon Karl, Martha Raddatz, thanks very much.

This transcript has been automatically generated and may not be 100% accurate.

U.S. contemplates humanitarian air drops over Iraq as humanitarian crisis worsens.

Obama Authorizes Targeted Strikes in Iraq

Insurgent forces have been taking over cities in northern Iraq.

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